Low loss venturi tube



Match 22, 1955 5, BALL 2,704,555

LOW LOSS VENTURI TUBE Filed June 11, 1951 2 Shets-Sheet 1 FIG-2'.

United States Patent Low Loss VENTURI TUBE Horace Edward Dall, Luton,England, assignor to George llxient Limited, London, England, a companyof Great ritain Application June 11, 1951, Serial No. 230,997 Claimspriority, application Great Britain June 23, 1950 9 Claims. (Cl. 138-44)This invention is an improved Venturi tube of the compact steep-angledtype for insertion between an inlet and outlet pipe to produce adiflerential pressure for measurement of fluid flow.

In previously known Venturi tubes of this type such as that described inBritish specification No. 473,562 (Nathan), the inlet and outlet angleswere made steeper and the throat joining them was made shorter than withthe orthodox type of Venturi, and as a result there was obtained a loweroverall pressure loss and a simpler and more compact device.

We have found that, if a particular relationship is made between theinlet pipe size, the mouth diameter of the inlet cone and the throatlength, and if the inlet and outlet angles are within a certain range ofvalues, the discharge coefficient instability which was experienced withthe previous device is largely eliminated, and a stable coeflicientobtained over the usual range of Reynolds fiumbers, together with aneven lower overall pressure oss.

The Venturi tube according to the invention comprises two truncatedcones with smaller ends adjacent which are separated by a throat oflength between 0.03d and 0.1a where d is the diameter of the throat, theinlet cone having an included angle between 40 and 50, the outlet conehaving an included angle between 12 and 17, the arrangement being thatthe area of flow abruptly changes between the inlet pipe and the inletcone, and the mouth diameter Dm of the inlet cone being related to thediameter D of the inlet pipe and the diameter d of the throat inaccordance with the equation where k is 0.5-0.75. The preferred coneangles are substantially 45 and 15 respectively, and the preferredlength of the throat is 0.0611. The abrupt change of area of flow may beefiected by locating between the mouth of the inlet cone and the innerperiphery of the inlet pipe a wall which is substantially radial.

It has been found advantageous to connect the mouth of the outlet coneto the smaller end of a further truncated cone having an included angleless than that of the outlet cone. Alternatively, the outlet cone can beconnected in the same way with two or more outwardly diverging truncatedcones in series, having included angles progressively decreasing fromthat of the outlet cone. By these means the fluid is brought bygradually by progressively decreasing inclines from the throat to theoutlet pipe.

If one considers the hypothetical provision of an infinitely largenumber of outlet cones in series each of infinitely small length, aconcave curve is achieved. Thus, in a modification of the invention, theoutlet cone is concave from the smaller end to the larger end, thetangents to the curved wall at the smaller end having an included anglebetween 12 and 17.

In the preferred form of the device, the higher pressure ofltake islocated in the wall of the inlet pipe immediately adjacent to theposition of the said abrupt change in area of fluid flow and the lowerpressure offtake is located entirely within the said throat. Theseofitakes may be in the form of slots, holes or annular recesses.Especially at extremely low values of the throat length it may benecessary to utilise for the low pressure oiftake an annular recesssurrounding the throat.

In one embodiment of the invention the lower pressure offtake may beconnected to an annular space surice rounding the throat, e. g. betweenthe backs of the cones and a casing enclosing the cones. A pipe may thenbe provided to connect this annular space to a difierential gauge. Thebacks of the cones may be connected and strengthened by struts or ribsinside the said annular space.

The invention is illustrated diagrammatically in the accompanyingdrawing, in which:

Figure 1 is a section of one form of a Venturi tube attachment adaptedfor difierential pressure measurement of fluid flow; and

Figures 2, 3 and 4 are respectively a first, second and thirdmodification of the same.

In Figure 1, a Venturi attachment 1 is adapted to be inserted between aninlet pipe 2 and an outlet pipe (not shown in Figure 1). At the inletend of the attachment 1 is a cylindrical chamber 3 of the same diameteras that of the inlet pipe 2 and forms an extension thereof. In thischamber 3 is a higher pressure ofltake consisting of a comparativelynarrow bore 4 and a comparatively wide tapping 5. An inlet cone 6 has amouth 7, located in an obstructing end wall 8 of the chamber 3, andterminates in a throat 9. An annular space 10 is formed in the maincasing round the throat 9 and is connected to the space enclosed by thethroat by an annular recess 11 formed in the throat wall leaving smalllands 12 in said wall on either side of the recess 11 in order to avoida sharp angle. These lands are accentuated in the drawing for clarity. Alower pressure otftake 13 is located in the space 10. An outlet cone 14extends from the throat 9 on the side remote from the inlet cone 6.

In Figure 2, a further outlet cone 15 is connected to the downstream endof the outlet cone 14. The outlet cone 15 has a smaller included anglethan that of the outlet cone 14. An outlet pipe 16 is shown secured tothe outlet cone 15.

In Figure 3, three further outlet cones 17, 18, 19 are connected inseries to the downstream end of the outlet cone 14, the cones 17, 18, 19having included angles progressively decreasing from that of the outletcone 14.

In Figure 4, the outlet cone 14 is concave from the smaller end to thelarger end, the tangents to the curved wall at the smaller end having anincluded angle of 15.

Besides obtaining a stable discharge coefficient, the improved Venturitube has an extremely low overall pressure loss averaging only 5 or 6%of the differential pressure for tubes of medium proportion, which lossis between 2 and 3 times less than for an orthodox type of venturi tube.

I claim:

1. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the diflerential pressure measurement of fluid flow, comprising twotruncated cones with smaller ends adjacent which are separated by athroat of length between 0.03d and 01d where d is the diameter of thethroat, the inlet cone having an included angle between 40 and 50, theoutlet cone having an included angle between 12 and 17, the mouthdiameter Dm of the inlet cone being related to the diameter D of theinlet pipe and the diameter d of the throat in accordance with theequation Dm d =k(D d where k is 05-075, and a Wall disposed between andjoining the mouth of the inlet cone and the inner periphery of the inletpipe, said wall forming an abrupt obstruction to the fluid flow.

2. A Venturi tube as claimed in claim 1 in which the inlet cone has anincluded angle of about 45.

3. A Venturi tube as claimed in claim 1 in which the outlet cone has anincluded angle of about 15.

4. A Venturi tube as claimed in claim 1 in which the length of thethroat is about 0.06.

5. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the difierential pressure measurement of fluid flow, comprising twotruncated cones with smaller ends adjacent which are separated by athroat of length between 0.03a' and 0.1d Where d is the diameter of thethroat, the inlet cone having an included angle between 40 and 50, theoutlet cone having an included angle between 12 and 17, the mouthdiameter Dm of the inlet cone being related to the diameter D of theinlet pipe and the diameter d of the throat in accordance with theequation Dm -d =k(D -d-), where k is 0.5-0.75, and a substantiallyradial wall joining the mouth of the inlet cone and the inner peripheryof the inlet pipe.

6. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the differential pressure measurement of fluid flow, comprising twotruncated cones with smaller ends adjacent which are separated by athroat of length between 0.03d and 0.141 Where d is the diameter of thethroat, the inlet cone having an included angle between 40 and 50, theoutlet cone having an included angle between 12 and 17, the mouthdiameter Dm of the inlet cone being related to the diameter D of theinlet pipe and the diameter d of the throat in accordance with theequation Dm -d =k(D d where k is 0.50.75, a wall disposed between andjoining the mouth of the inlet cone and the inner periphery of the inletpipe, said wall forming an abrupt obstruction to the fluid flow, and afurther truncated cone having an included angle less than that of theoutlet cone, the mouth of the outlet cone being connected to the smallerend of the said further truncated cone.

7. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the differential pressure measurement of fluid flow, comprising twotruncated cones with smaller ends adjacent which are separated by athroat of length between 0.0311 and 0.10 where d is the diameter of thethroat, the inlet cone having an included angle between 40 and 50, theoutlet cone having an included angle between 12 and 17, the mouthdiameter Dm of the inlet cone being related to the diameter D of theinlet pipe and the diameter d of the throat in accordance with theequation Dm -d =k(D d where k is 0.5-0.75, a wall disposed between andjoining the mouth of the inlet cone and the inner periphery of the inletpipe, said wall forming an abrupt obstruction to the fluid flow, and aplurality of outwardly diverging truncated cones in series connected tothe outlet cone, the said outwardly diverging truncated cones havingincluded angles progressively decreasing from that of the outlet cone.

8. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the differential pressure measurement of fluid flow, comprising twotruncated cones with smaller, ends adjacent which are separated by athroat of length between 0.03d and 01:1 where d is the diameter of thethroat, the inlet cone having an included angle between 40 and the innerwall of the outlet cone being concave from the smaller end to the largerend, the tangents to the curved wall at the smaller end of the outletcone having an included angle between 12 and 17, the mouth diameter Dmof the inlet cone being related to the diameter D of the inlet pipe andthe diameter d of the throat in accordance with the equation where k is0.5-0.75, and a wall disposed between and joining the mouth of the inletcone and the inner periphery of the inlet pipe, said wall forming anabrupt obstruction to the fluid flow.

9. A Venturi tube for insertion between an inlet pipe and an outlet pipefor the differential pressure measurement of fluid flow, comprising twotruncated cones with smaller ends adjacent which are separated by athroat of length between 0.03d and 0.1:! where d is the diameter of thethroat, the inlet cone having an included angle between 40" and 50, theinner wall of the outlet cone being concave from the smaller end to thelarger end, the tangents to the curved wall at the smaller end of theoutlet cone having an included angle between 12 and 17, the mouthdiameter Dm of the inlet cone being related to the diameter D of theinlet pipe and the diameter d of the throat in accordance with theequation Dm -d =k(D -d where k is 0.5-0.75, and a substantially radialwall joining the mouth of the inlet cone and the inner periphery of theinlet pipe.

References Cited in the file of this patent UNITED STATES PATENTS1,802,766 Kerr Apr. 28, 1931 FOREIGN PATENTS 418,349 Germany Sept. 5,1925 473,562 Great Britain Oct. 15, 1937

